The present invention generally relates to a method for in-situ removal of unwanted film layers from a semiconductor substrate and more particularly, relates to a method for in-situ removal of photoresist layers and sidewall polymers from a surface of a wafer in a photoresist strip chamber by adding a magnetic field in the chamber to increase the ion energy of the plasma ions generated such that both the photoresist layers and the sidewall passivation layers of polymer are removed simultaneously.
In the fabrication of semiconductor devices, various processing steps are started with a photolithography process for defining a circuit on the wafer. For instance, in modern memory devices, many layers of metal conductors are required for providing a multi-layer metal interconnection structure. As the number of layers of metal interconnections increase, and as the device geometry is continuously being reduced to allow more densely packed circuits, the photolithography process required to define patterns of circuits becomes more complicated and difficult to carry out.
In a process for forming metal vias or lines on an insulating layer on a wafer, not only must also be removed. The sidewall passivation layer is normally used to enhance the etch directionality and to improve the anisotropy. It is carried out by adjusting an etchant gas composition and reactor parameters such that an etch-inhibiting film can be formed on the vertical sidewalls of a via or hole. The passivation film slows down or completely stops lateral etching by the etchant gas while the etching of horizontal surfaces continues. Any oxide growth is prevented on horizontal surfaces since the surfaces are exposed to ion bombardment. Similarly, sidewall passivation films can be deposited by choosing a greater elemental ratio or carbon to fluorine in a fluorocarbon plasma. When a suitable chemistry is selected, involatile polymer films can be deposited on the sidewalls of via or line cavities to form a coating that blocks attack from etchant gas. While polymer film may also deposit on the horizontal surfaces, the film is removed by ion bombardment and thus allowing a continuing etching of such surfaces. The sidewall passivation is a very useful method for preserving linewidth control especially when an isotropic etchant such as fluorine or chlorine gas is used.
After a via or line etching process is completed, the sidewall passivation layer of a polymeric material must be removed before the wafer can be further processed. In a conventional method, the sidewall polymer cannot be removed in a photoresist strip chamber where only a microwave or a decoupled source plasma is used for stripping photoresist layer after metal etching. Such a photoresist strip process does not remove sidewall polymer films that was formed for sidewall passivation. It is therefore necessary to subject the wafer to a separate wet etching process for removing the sidewall polymer. For instance, a wet stripper process can be implemented after a photoresist stripping process by utilizing wet etchant such as ACT(copyright) 690C or EKC(copyright) 265 to remove the sidewall polymer after a metal etching process and a photoresist strip process. The ACT(copyright) 690C is a mixture of DMSO (dimethyl-sulphur-oxide), MEA (mono-ethyl-amine) and catechol, while EKC(copyright) 265 is a mixture containing HDA (hydroxy-amine). The wet etching process is both time consuming and may cause other problems to the circuits already formed on the wafer surface. Moreover, as the device dimension is gradually reduced to the 0.25 xcexcm scale, the sidewall polymer passivation layer becomes more difficult to remove in a wet stripping process due to the reduced via size or linewidth in those devices.
It is therefore an object of the present invention to provide a method for in-situ removal of unwanted coating layers from the surface of a semiconductor substrate without the drawbacks or the shortcomings of the conventional method.
It is another object of the present invention to provide a method for in-situ removal of unwanted coating layers from the surface of a semiconductor substrate in a photoresist strip chamber.
It is a further object of the present invention to provide a method for in-situ removal of unwanted coating layers from a semiconductor substrate in a photoresist strip chamber equipped with magnetic field enhancement.
It is another further object of the present invention to provide a method for in-situ removal of photoresist and sidewall polymer from a wafer surface in a photoresist strip chamber by switching on a magnetic field having a substantially constant flux density and maintaining such field until substantially all unwanted films are removed from the wafer.
It is still another object of the present invention to provide a method for in-situ removal of photoresist and sidewall polymer from a wafer surface by producing a magnetic field in a photoresist strip chamber and maintaining a flux density of at least 10 gauss.
It is yet another object of the present invention to provide a method for in-situ removal of photoresist and sidewall polymer from a wafer surface by subjecting the wafer to an oxygen plasma which has increased ion energy by switching on a magnetic field.
It is still another further object of the present invention to provide a method for removing unwanted coating layers from a wafer surface by subjecting the wafer to plasma ions of substantially oxygen in a magnetic field that has a flux density of at least 10 gauss.
It is yet another further object of the present invention to provide a method for in-situ removal of unwanted coating layers from a pre-processed semiconductor substrate by subjecting the semiconductor substrate to an oxygen plasma maintained in a magnetic field having a flux density of at least 20 gauss for a time period of not less than xc2xd minute.
In accordance with the present invention, a method for in-situ removal of layers of photoresist and sidewall polymer from a wafer surface is provided.
In a preferred embodiment, a method for in-situ removal of photoresist and sidewall polymer from a wafer surface can be carried out by the operating steps of first positioning a pre-processed wafer in a process chamber, flowing an etch gas into the chamber, igniting a plasma and generating plasma ions of the etch gas, producing a magnetic field which has a substantially constant flux density, and maintaining the substantially constant flux density for a predetermined length of time until substantially all photoresist and sidewall polymer are removed from the wafer.
The etch gas may include oxygen, or oxygen and water, or oxygen, water and nitrogen. The pre-processed wafer may have metal lines defined on top. The plasma ions generated may be substantially oxygen ions. The substantially constant flux density is at least 10 gauss, or between about 10 gauss and 100 gauss. The predetermined length of time is at least xc2xd minute, or between about xc2xd minute and about 10 minutes. The substantially constant flux density may be 20 gauss which is maintained for a length of time of about 3 minutes.
In another preferred embodiment, the present invention method for removing unwanted coating layer from a wafer surface can be carried out by first providing a pre-processed wafer that has unwanted coating layers on top in a process chamber, flowing an etch gas including oxygen into the process chamber, igniting a plasma in the etch gas and generating plasma ions of substantially oxygen, generating a magnetic field which has a flux density of at least 10 gauss in the chamber, and maintaining the flux density for a length of time until substantially all the unwanted coating layers are removed from the wafer.
The unwanted layers may include, but not limited to, photoresist coating layers and sidewall polymer passivation layers. The process chamber utilized may be a photoresist etch chamber. The etch gas may include oxygen and water, or oxygen, water and nitrogen. The magnetic field generated may have a flux density of between about 10 gauss and about 100 gauss. The length of time that the wafer is exposed to the magnetic field enhanced plasma is at least xc2xd minute.
In still another preferred embodiment, a method for in-situ removal of unwanted coating layers from a pre-processed semiconductor substrate can be carried out by the steps of positioning a pre-processed semiconductor substrate in a plasma etch chamber, flowing an etch gas that includes oxygen into the chamber, igniting a plasma and generating plasma ions of substantially oxygen, switching on a magnetic field to produce a flux density of at least 10 gauss, and increasing the ion energy of the plasma ions of substantially oxygen and maintaining such energy for a length of time until the unwanted coating layers are removed from the pre-processed semiconductor substrate. The flux density generated by the magnetic field may be between about 10 gauss and about 100 gauss.